E9

E9 or E-9 may refer to:
* "E"₉, the special Lie algebra
* E9 tuning, a common tuning for steel guitar necks of more than six strings
* EMD E9, a diesel locomotive
* European route E9
* London E9, the postcode for Homerton

and also :
* E9, the Sungai Besi Expressway
* IATA code for Boston-Maine Airways is E9
* E-9A Widget, U.S. Air Force range control aircraft
* E-9, a U.S. Military pay grade